| Summary: | 碩士 === 國立台灣工業技術學院 === 營建工程技術研究所 === 85 === This study investigates the properties and behaviors of normal
concretewith fly ash subjectd to elevated temperature. During
the research,appropriatefly ash content,fly ash substitution
method,and concrete mix design method are selected to find the
reasonable proportions of normal concrete with fly ash.Large
amount of samples are then produced from the reasonable
proportions of normal concrete with fly ash,to test and to study
the effects of "ExposedDuration of High Temperature" and
"Recovery Duration of Heat Release" on the mechanical properties
and behaviors of the concrete with fly ash.An analysison the
elevated temperature properties and rehydration on concrete with
fly ashis also conducted. The results show that under 400℃,
concrete with fly ash revealed a contractingphenomenon.However,
at 600℃,concrete expansion occurred due to the expansion
ofsilicon aggregates,expansion is higher at 800℃.Unit weight of
concrete show adecreasing trend along with the increase in
exposed duration and temperature.Ultrasonic pulse-wave speed
decreases with the increased in temperature and exposed
duration.These revealed that voids and cracks increase in
exposed duration.At 200℃∼400℃,dynamic modulus of elasticity
of concrete with fly ash is larger then normal concrete.However
at 600℃∼800℃,dynamic modulus of elasticity of normal concrete
without fly ash is larger than concrete with fly ash.
Compressivestrength at 200℃ is larger than at room temperature.
Along with the increase intemperature and exposed duration,
strength of concrete decreases.In terms of recoveringcondition
after heat release,rehydration is best and strength recovery
rate islargest under water recovery.The C-S-H formed by
rehydration has a function offilling the voids and cracks as
well as strength the matrix. Void Index Measurement(VIM)
increased with the increase of exposed duration ofhighest
temperature.Void index of concrete with fly ash is relatively
smaller thannormal concrete without fly ash.However,at 600℃
∼800℃,void index of concretewith fly ash is relatively larger
than normal concrete without fly ash.Generallyspeaking,elevated
temperature resistance of normal concretewith fly ash is
notbetter than normal concrete without fly ash.
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